This invention relates to an apparatus for detecting positions illuminated by a light beam by using light receiving elements and, more particularly, to light detecting apparatus of improved resolution of displacements.
A light detecting apparatus using light receiving elements has been used to detect the movement or displacement of a movable body such as a working blade of an earth moving equipment. In such apparatus, a plurality of light receiving elements or photoelectric transducers are arranged on the movable body for detecting the position irradiated by a light beam by projecting the light beam upon the array of the light receiving elements thereby causing a particular light receiving element illuminated by the light beam to generate an electric signal. However, according to the prior art light detecting apparatus, since the electric signal generated by the light receiving elements in this manner is used directly as an illuminated position detection signal, the resolution of the displacement has been limited by the spacing between the light receiving elements and the width illuminated by the light beam. The term "resolution of displacement" is used herein to represent a minimum unit of the displacement that can be detected so that as the resolution is increased, the accuracy of detection can also be improved.
More particularly, with the prior art arrangement, when the spacing between adjacent light receiving elements H is represented by X cm, the resolution will be given by X cm, as diagrammatically shown in FIG. 1a. Accordingly, when the displacement to be detected is 3X cm, the displacement is detected in three steps. Further, in order to obtain such resolution, the width of the light beam should be limited such that the beam will not illuminate two or more light receiving elements at the same time. Accordingly, where the source of the light beam is spaced considerably from the light receiving elements as in the case wherein the light detecting apparatus is used for automatic level adjustment of a bulldozer or a grader, the width of the light beam increases when it impinges upon the light receiving elements with the result that sufficiently high detection accuracies can hardly be obtained.
In the prior art apparatus, it is possible to improve the resolution only by decreasing the spacing between adjacent light receiving elements, but this measure increases the number of the light receiving elements. Since these light detecting apparatus are generally used in the outdoor, it is necessary to provide expensive interference filters or the like for responsive light receiving elements for the purpose of improving the signal to noise ratio with respect to the sun light. This also increases the number or component elements and the cost of the apparatus.